Effect of seed coat colour on seed storability in sorghum genotypes (Sorghum bicolor (L.) Moench)

Introduction

Sorghum [Sorghum bicolour (L.) Moench] is a tropical cereal C 4 grass plant belonging to Poaceae family. Sorghum is also called as camel crop due to its high tolerance to water and temperature stress and also high photosynthesis efficiency. It is an important grain and forage crop of semiarid regions due to its high adaptability and suitability to rain-fed low input agriculture (Anagholi et al., 2000) [3] . It is one among the most efficient crops in conversion of solar energy and use of water and is known as a high-energy and drought tolerant crop that is environmentally friendly. Sorghum is the fifth most important cereal in the world followed by maize, rice, wheat and barley covering an area of about 41.97 million ha with production of 65.21 million metric tonnes and productivity of 1.45 metric tons per ha. India is a major sorghum growing country in the world, ranks third in acreage and seventh in production next to United States of America. It is cultivated in 4.24 million ha with an annual production of 4.78 million metric tons of grain with productivity of 1130 kg/ha (Anon., 2022 a) [5] . In India, it is cultivated in Maharashtra, Karnataka and Andhra Pradesh as a rainfed crop. In Karnataka, sorghum production is about 1.41 million ha with a production of 1.13 million metric tons and productivity of 974 kg/ha. Major sorghum growing districts of Karnataka are Kalaburgi, Raichur, Koppal, Belagavi and Vijayapur (Anon., 2022b) [5] . Seed coat is vital input in seed production and it attains their specific colour at physiological maturity. Seed coat colour is simple and excellent indicator of seed quality parameters. One of the unique features of sorghum seed is its variation in seed colour (Tiriyaki et al., 2016). Differences in seed coat colour have been associated with differences in the composition of chemical compounds in the seed coats. Seed storage and retention of seed viability is an important postharvest operation that decides the success of seeds in the next generation. Seed deterioration begins immediately after physiological maturity and is reflected in terms of loss in viability and vigour. Seed coat acts as a major defence against harmful environmental conditions and protect embryo from mechanical stress and from temperature and humidity fluctuation during storage. Seed coat is the main modulator of interaction between the internal structures and the external environment. It not only preserves integrity of seed parts but also protects the embryo from mechanical injuries and attacks of pest and diseases. So, seed coat is having the central role in seed longevity as it is the primary defence against adverse environmental condition.

Materials and Methods

A laboratory experiment was conducted in Department of Seed Science and Technology, College of Agriculture, Raichur during 2020-21, to know influence of seed coat colour on longevity of sorghum. The experiment was laid in a completely randomised design. There were 20 genotypes, white (G 1, G 2, G 3 ), pearly white (G 4 , G 5 ), chalky white (G 6 ), whitish purple (G 7 ), purple(G 8 ), yellow (G 9 ), red (G 10 , G 11 ), light red (G 12 , G 13 , G 14 ), light brown (G 15 , G 16 ), dark brown (G 17 , G 18 ), black (G 19 , G 20 ). The seeds were harvested during February 2021. They were dried at 10 per cent moisture level and kept for storage under ambient condition in the month of August. These seeds were used for testing seed quality parameters.

One hundred seeds from each replication were taken from each treatment. They were kept for germination as per ISTA (2025) [9] and number of germinated seed was counted as per the formula

From the germination test, on 10 th day, ten normal seedlings were selected randomly from each treatment and the shoot length was measured and was expressed in centimetre.

From the germination test, on 10 th day, ten normal seedlings were selected randomly from each treatment and the root length was measured and was expressed in centimetre.

Seedling vigour index (SVI-I)

The seedling vigour index -I was calculated as per the method followed by Abdul-Baki and Anderson (1973) [1] .

Seedling vigour index (SVI-II)

The seedling vigour index-II was worked out by multiplying the per cent seed germination and mean seedling dry weight (Abdul-Baki and Anderson, 1973) [1] .

Electrical conductivity (dSm -1 ) Seeds were soaked overnight by keeping in an incubator maintained at 25 °C ± 1 for twelve hours. The seed leachate was collected and measured in digital conductivity bridge with a cell constant 1.0 and the mean values were expressed in deci Siemens per meter (dSm -1 ) as described by Milosevic et al., 2010 [11] .

Results and Discussion

Seed coat colour is unique genetic factor that varies with crop in most cases and sometimes with varieties. Seed coat colour has been coined as a factor of seed quality (Vakeswaran, 1998) [17] and seed coat colour variation has been related to seed quality variations. Seed longevity is seed viability after seed dry storage (Rajjou and Debeaujon, 2008) [14] . Ageing of seed is well recognized cause of differences in seed quality in all species (Powell et al, 1984) [13] . Seed deterioration and seed ageing are inexorable and irreversible process. In present investigation, the seed quality parameters declined with increase in storage period. Among the different seed coat colour sorghum genotypes, black seed coat colour genotype G 20 recorded significantly highest germination both at initial and at the end of ten months of storage (95.50% and 80.00% respectively). Whereas white seed coat colour genotype recorded lowest germination both at initial (84.53%) and at the end of the storage period (69.00%) (Table 1). This might be due to the presence of some various phenolic compounds in unpigmented seed that block the metabolism preparatory to germination and prevent the access of oxygen to embryo The highest shoot (20.61 cm and 17.60 cm) and root length (12.13 cm and 8.20 cm) was noticed in black seed coat colour genotype, G 20 both at the beginning and at the end of the storage period respectively. While the lowest shoot (10.00 cm and 5.70 cm) root length (10.06 cm and 3.00 cm) (Table 2) was observed in white seed coat colour sorghum genotypes. The highest seedling length in pigmented seed might be because of its bolder size that may contain greater metabolites for resumption of embryonic growth and better accumulation of nutrients during germination. Similar results were also recorded by Anuradha et al. (2009) [6] in chickpea, Sinefu et al. (2011) [15] in bambara groundnut and Ibrahim in red clover. As germination alone may not reveal the real potential of seed lots, so assessment of seedling vigour index is of prime importance. The highest seedling vigour index-I (3127 and 2064) and seedling vigour index-II (15805 and 11480) was noticed by black seed coat colour genotype G 20 both at initial and at the end of the storage period. Whereas white seed coat colour sorghum genotype recorded lowest vigour indices at initial and after ten months of storage [(1696 and 600) and (13305 and 8625) respectively] (Table 3). The highest seedling vigour index-I in black seed coat genotype might be due to highest seedling length, germination percentage and speed of germination. The findings are line with Abdullah et al. (1988) [2] in long bean, Mokashi (2017) [12] in cowpea. Black seed coat colour genotype recorded significantly lowest electrical conductivity at the beginning and at the end of storage period (0.10 dSm -1 and 0.24 dSm -1 ) whereas white seed coat colour genotype recorded significantly highest electrical conductivity at initial and at the end of storage period (0.15 dSm - 1 and 0.39 dSm -1 ) (Fig. 1). The highest electrical conductivity in white or unpigmented genotypes was attributed to thinner seed coat leading to rapid water uptake into the outer cells of cotyledons that might disrupts the cell membranes and resulting in high solute leakage from the embryo. These observations are in accordance with Capeleti et al. (2005) [7] in soybean, Ibrahim in red clover, Mokashi (2017) [12] in cowpea and Kumar et al. (2020) [10] in soybean.

Conclusion

All the pigmented seeds recorded significantly higher seed quality attributes. Among the genotypes, black seed coat colour genotype G 20 -IS25040 and the dark brown colour genotype G 17 -IS37255 maintained its seed quality up to the ten months of storage which is above the Indian minimum seed certification standards. Hence these two genotypes were found to be superior in maintaining seed quality during storage.

References

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